My Imaginary Friend

I looked out of my window at the sea. It was low tide, and the waves rolled gently up against the shore. The sun was setting, and its soft light was reflected off the clear blue water. I had been living here my whole life, and still I was stunned by the beauty of the land and sea. I breathed in the salty air, and thought about all the waves I would surf tomorrow.
"It's so beautiful." I said to myself softly.
"It really is." said a voice from behind me.
I didn't recognize the voice, nor did I recognize the person as I whipped around to face them.
"Who are you?" I said as my stomach twisted up in fear.
"I'm Susan." said the girl. "And I'm your new imaginary friend."